abstract
Several strong-motion seismograms recorded at 8 km from a large nuclear test at Pahute Mesa, Nevada Test Site, are modeled using the Cagniard-de Hoop technique. The ratio of vertical to radial motions suggest that the peak values are produced by ray paths that penetrated to a depth several kilometers below the source. A homogeneous layered Earth model with velocity increasing with depth was used in the modeling of the velocity time histories. The upper portion of the velocity model was determined by averaging bore-hole data and the lower portion was obtained from regional refraction measurements. Assuming a modified Haskell (1967) source representation,
ψ ( t ) = ψ o [ 1 − e − K t ( 1 + K t + ( K t ) 2 / 2 − B ( K t ) 3 ) ]
we obtain a range of source descriptions with ψ0 varying with K and B, ψ0 (K,B). The range of source models for Jorum are ψ0 (5, 1) = 3.1, ψ0 (5, 2) = 1.7, and ψ0 (5, 3) = 1.2 times 1011 cm3, respectively. Given an explosion source description, it is a straightforward task to determine the teleseismic attenuation from WWSSN observations. From both the short- and long-period observations from these events, an average t* of 1.3 is obtained for compressional waves of a dominant 1-sec period. This estimate is insensitive to the range of K and B obtained from the near-field modeling.
Near-field modeling in Frenchman Flat, Nevada Test Site
